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P波初动符号物理图像明确,是稳定的地震波信息.在资料充分时,可以较好地确定震源机制解.网格搜索法是目前流行的利用P波初动符号求解地震震源机制解的方法.不过,在实际观测资料不充分时,虽然较迭代算法优越,但网格搜索法依然有较大的不确定性.到目前为止,人们还没有找到合理的解决方案,极大地制约了这一类方法的应用.针对这一现状,本文在许忠淮提出的格点尝试法的基础上对网格搜索法进行了几个方面的改进.首先,采用新的加权方法计算加权矛盾比:权重因子包括反映初动符号质量的权重以体现资料质量的影响;不包括反映观测点与节面距离的权重以避免因节面附近资料权重的双重减小带来的系统偏差;通过减小震源球上密集资料点的权重以部分地抵消震源球上P波初动符号资料分布不均匀对可能解的影响.在通过加权矛盾比筛选可能的震源机制解时,把震源球分为面积相对均匀的网格进行解的搜索,避免了因网格划分不均匀所导致的平均解的计算偏差.针对资料不足情况下震源机制解会受控于个别观测点P波初动符号的情况,我们借鉴杰克刀(jackknife)技术,在可选解中增加了那些一个观测点被去除后的可选解,既对解的质量有了更好的把握,又增加了找到真解的可能性.进一步地,针对可选解存在多个解簇的情况,本文提出了通过聚类提供多组可选解的做法.最后,针对目前缺乏对解的合理评价体系的现状,提出了主要基于解的离散度并参考加权最小矛盾比对震源机制解质量进行评价的新方案. 相似文献
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动态遗传算法及其在P波初动震源机制解中的应用 总被引:9,自引:0,他引:9
利用动态遗传算法对P波初动震源机制解进行反演计算,并与前人常用的反演计算方法对比,认为遗传算法在P波初动 震源机制解中的应用是有很有效的。 相似文献
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简要叙述运用P波初动资料确定地震震源机制(断层面解)的原理与方法,并以图解法为例,详细阐述相关的物理概念及求地震震源机制解的具体步骤,以适应具有不同专业背景(例如:地震学、地球物理学、地质学、大地测量学、工程地震学、灾害科学、管理科学)的不同读者(例如:学生、教师、管理人员)的不同需求(例如:了解、学习、应用). 相似文献
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用Pg波初动求解中小地震的震源参数 总被引:1,自引:0,他引:1
依据震源理论,根据我国数字化地震台网目前的实际情况,在前人研究成果的基础上,提出一种用Pg波初动求中小地震震源参数的实用方法.可以用三个台的Pg波初动(初动峰值和峰值时间),较简便地计算出地震的震源参数, 从而为以震源和介质动态变化为依据的地震预报,提供一个用于日常监测预报的方法. 相似文献
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求震源机制P波初动解的格点尝试概率法 总被引:9,自引:0,他引:9
考虑到P波初动数据在震源球面上分布的不均匀性对节面解的可能影响,不用矛盾符号所占比例的大小作为选择可取节面解的标准,而是将震源球面分成许多小块,再确定有P波初动数字的小块为正号区或负号区的概率,最后以全部有数据小块的平均概率的高低作为选择解答的标准。用此改进方法重新测定了徐纪仁等(Xu et.al,,1988)发表的青藏高原地区99个地震的震源机制解,从中筛选出了20个可信的解答。 相似文献
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本研究利用CAP方法反演得到了2013—2017年辽宁地区19个3.5级以上地震的震源机制解.结果显示辽宁地区地震的震源机制以走滑类型为主,P轴和T轴方位分别集中在北东东和北北西方向,分别与区域构造应力场主压和主张应力方向一致.矩心深度结果反映辽宁地区在地壳内各个深度的位置都可能孕震,而以地壳中部最为活跃.灯塔地区地壳极浅部曾发生中等强度的地震,在地震减灾工作中需要引起注意.而盖州地区地壳底部仍有少量地震,显示其附近岩石仍具有脆性特性,且该处邻近一级块体边界,贯穿地壳的断层导致下地壳也有地震发生.震源机制结果显示区域构造应力场对辽宁地区大部分地震的发生有着主导作用,在局部地区复杂的断层构造也会对震源机制产生较大影响. 相似文献
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本研究利用CAP方法反演得到了2013—2017年辽宁地区19个3.5级以上地震的震源机制解.结果显示辽宁地区地震的震源机制以走滑类型为主,P轴和T轴方位分别集中在北东东和北北西方向,分别与区域构造应力场主压和主张应力方向一致.矩心深度结果反映辽宁地区在地壳内各个深度的位置都可能孕震,而以地壳中部最为活跃.灯塔地区地壳极浅部曾发生中等强度的地震,在地震减灾工作中需要引起注意.而盖州地区地壳底部仍有少量地震,显示其附近岩石仍具有脆性特性,且该处邻近一级块体边界,贯穿地壳的断层导致下地壳也有地震发生.震源机制结果显示区域构造应力场对辽宁地区大部分地震的发生有着主导作用,在局部地区复杂的断层构造也会对震源机制产生较大影响.
相似文献13.
山东及附近区域部分中小地震震源机制特征分析 总被引:1,自引:0,他引:1
收集了2001~2006年4月山东及周边省记录的20次(其中有8次地震为2003年青岛震群地震)中等地震波形资料。并对上述地震进行了重新定位。根据各台站记录的P波、SV波、SH波初动和它们之间的振幅比,利用Snoke联合计算地震震源机制解的程序,计算了20次地震震源机制解。就所研究的震例来看,断层破裂错动方式以近于走滑错动为主,在NE向断裂上为右旋错动,在NW向断裂上为左旋错动。大部分地震发生在现有断裂上,并且破裂方向与其断裂构造相吻合,这表明,现有断裂构造对中小地震的破裂方式有控制作用。 相似文献
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The distribution of the focal mechanisms of the shallow and intermediate depth (h>40 km) earthquakes of the Aegean and the surrounding area is discussed. The data consist of all events of the period 1963–1986 for the shallow, and 1961–1985 for the intermediate depth earthquakes, withM
s
5.5. For this purpose, all published fault plane solutions for each event have been collected, reproduced, carefully checked and if possible improved accordingly. The distribution of the focal mechanisms of the earthquakes in the Aegean declares the existence of thrust faulting following the coastline of southern Yugoslavia, Albania and western Greece extending up to the island of Cephalonia. This zone of compression is due to the collision between two continental lithospheres (Apulian-Eurasian). The subduction of the African lithosphere under the Aegean results in the occurrence of thrust faulting along the convex side of the Hellenic arc. These two zones of compression are connected via strike-slip faulting observed at the area of Cephalonia island. TheP axis along the convex side of the arc keeps approximately the same strike throughout the arc (210° NNE-SSW) and plunges with a mean angle of 24° to southwest. The broad mainland of Greece as well as western Turkey are dominated by normal faulting with theT axis striking almost NS (with a trend of 174° for Greece and 180° for western Turkey). The intermediate depth seismicity is distributed into two segments of the Benioff zone. In the shallower part of the Benioff zone, which is found directly beneath the inner slope of the sedimentary arc of the Hellenic arc, earthquakes with depths in the range 40–100 km are distributed. The dip angle of the Benioff zone in this area is found equal to 23°. This part of the Benioff zone is coupled with the seismic zone of shallow earthquakes along the arc and it is here that the greatest earthquakes have been observed (M
s
8.0). The deeper part (inner) of the Benioff zone, where the earthquakes with depths in the range 100–180 km are distributed, dips with a mean angle of 38° below the volcanic arc of southern Aegean. 相似文献
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Yuru Zhuo 《地震学报(英文版)》1992,5(1):33-43
Using the WKBJ approximation method we calculate the synthetic teleseismograms of P and PP waves to match the observed ones
of six large Chinese earthquakes with known focal mechanisms: Tibet earthquake of July 14, 1973; Haicheng earthquake of February
4, 1975; Songpan earthquakes of August 16, 1976, August 21, 1976 and August 23, 1976 and Nignhe earthquake of November 15,
1976. The focal mechanism of the Tibet earthquake is discussed to examine the technique used in the calculation.
We note that the amplitude ratios of PP and P waves (A
PP/A
P) have different characteristics for dip—slip events and strike—slip events within certain epicentral distances. We calculate
the synthetic teleseismograms of P and PP waves for the strike—slip and dip—slip events with fault angles of 330°, 240° and
0°, focal depths of 8 km, 17 km and 24 km, at the assumed station with an azimuth of 310° and epicentral distances from 40°;
to 80°. The diagrams of maximum amplitude ratios of PP and P waves (A
PP/A
P) versus distances are given. The possibility to use the (A
PP/A
P) values to give an approximate estimation for the focal mechanism type is discussed. This work may be useful for determining
the focal mechanism type for those earthquakes which have only few records such as the Chinese earthquakes from the 1930s
to 1960s.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 150–160, 1991. 相似文献
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Determining the focal mechanism of earthquakes helps us to better define faults and understand the stress regime. This technique can be helpful in the oil and gas industry where it can be applied to microseismic events. The objective of this paper is to find double couple focal mechanisms, excluding scalar seismic moments, and the depths of small earthquakes using data from relatively few local stations. This objective is met by generating three‐component synthetic seismograms to match the observed normalized velocity seismograms. We first calculate Green's functions given an initial estimate of the earthquake's hypocentre, the locations of the seismic recording stations and a 1D velocity model of the region for a series of depths. Then, we calculate the moment tensor for different combinations of strikes, dips and rakes for each depth. These moment tensors are combined with the Green's functions and then convolved with a source time function to produce synthetic seismograms. We use a grid search to find the synthetic seismogram with the largest objective function that best fits all three components of the observed velocity seismogram. These parameters define the focal mechanism solution of an earthquake. We tested the method using three earthquakes in Southern California with moment magnitudes of 5.0, 5.1 and 4.4 using the frequency range 0.1–2.0 Hz. The source mechanisms of the events were determined independently using data from a multitude of stations. Our results obtained, from as few as three stations, generally match those obtained by the Southern California Earthquake Data Center. The main advantage of this method is that we use relatively high‐frequency full‐waveforms, including those from short‐period instruments, which makes it possible to find the focal mechanism and depth of earthquakes using as few as three stations when the velocity structure is known. 相似文献
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利用区域波形数据使用CAP方法反演中强地震的震源机制正逐渐得到广泛应用.本文以胶东半岛近期发生的两次显著中等地震为例,讨论了使用CAP方法反演震源机制时的误差估计,展示了反演结果的不确定性分析过程.2013年11月23日和2014年1月7日在山东莱州和乳山分别发生了M4.6和M4.3级中等地震,两次事件均造成了较大影响.我们基于CAP方法,使用自助抽样(bootstrap)技术多次重复反演过程,得到大样本量的震源机制解数据;基于这些数据,使用粒子群算法和聚类分析技术给出了优化解,估计了震源机制解的误差范围,并利用震源机制解的P、T轴给出了震源球上的概率密度分布. 相似文献
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本文在对龙滩库区2006年9月30日至2013年5月26日发生的3682次地震进行精定位的基础上,利用FOCMEC方法和改进的格点尝试法反演了ML2.0以上地震震源机制及区域构造应力场,并综合龙滩库区地层岩性、断裂构造和渗透条件等资料,探讨了地震活动类型与库区蓄水过程的关系,获得以下认识:(1)龙滩水库蓄水后的地震活动主要丛集在罗妥、八茂、拉浪、坝首和布柳河5个深水区,地震类型以逆断为主,正断和走滑也占有一定比例.蓄水初期,库区地震类型呈现多样性,蓄水约4年3个月后,地震主要发生在浅部地层中,并大多为逆断型地震.(2)5个地震丛构造应力场最大主应力方向以NW-SE为主,倾角均较小,中等和最小主应力分布较凌乱,在此构造应力环境中,龙滩库区主要断裂整体上呈现走滑运动的性质,局部伴生不同程度的逆倾滑或正倾滑运动分量.(3)库区深、浅部地震活动水平和地震性质之所以会随蓄水过程发生变化,可能与深、浅部构造应力环境、岩体力学性质和渗透性能的差异有关. 相似文献
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Introduction Beijing and the adjacent regions is a significant seismically active area and many geoscien- tists have studied to different extents the non-elastic attenuation and source parameters in the area. GAO et al (1986) and ZHUO et al (1990) studied the coda Q in the Beijing region by the method of dominant frequency and mechanical frequency division with the simulated data. With the con- tinuous construction of digital seismic station network, the digital data are more favorably used… 相似文献